On July 23, 1914, Austria-Hungary delivered an ultimatum to the Balkan nation of Serbia. This ultimatum virtually guaranteed the outbreak of World War I only a few days later.

Nearly one month earlier Archduke Franz Ferdinand, the heir to the Austro-Hungarian throne, had been assassinated in the city of Sarajevo, in Bosnia and Herzegovina. The region had been annexed by the Austro-Hungarian empire only a few years earlier, a move that conflicted with the wishes of the Serbian government and people. The Serbians had hoped to annex Bosnia and Herzegovina as a prelude to the creation of a Greater Serbia, a large and powerful south Slav state in the Balkans.

In his book “The First World War: A Complete History” historian Martin Gilbert writes: “Serbia, landlocked since she first won independence several decades earlier as the first Slav State of modern times, wanted an outlet on the Adriatic, but was blocked by Austria. ... Bosnia could also serve as a military base, when need or opportunity arose, for an Austrian attack on Serbia.”

The head of Serbian military intelligence, Dragutin Dimitrijević, was instrumental in planning the assassination with a Serbian nationalist terrorist group, the Black Hand. Officially, Dimitrijević was careful to cover most of his tracks so as to maintain plausible deniability. Sometime in May, however, Serbian prime minister Nikola Pašić learned of the plot.

Historian Joachim Remak writes in his book “The Origins of World War I, 1871-1914”: “This knowledge confronted (Pašić) with a truly unenviable choice. If he were to tell the Austrians nothing and allow the assassination to proceed, he risked incurring the gravest of diplomatic crises and quite possibly war. If, on the other hand, he were to warn Vienna in an effort to prevent the plot from succeeding, he would in so doing have to admit just what sort of anti-Austrian activities had been tolerated on Serbian soil.”

Pašić limited himself to only a vague warning that the Archduke should cancel his visit to Sarajevo. The Austrians did not listen.

The Archduke's assassination on June 28 signaled a diplomatic crisis of the first magnitude. Over the preceding decades several diplomatic crises had unfolded, each threatening to start a general European war. Each had been weathered through negotiation, and though tempers ran high in the days after the murder, most Europeans believed that diplomacy would once again prevail.

At this time Europe was divided into two major power blocs. Germany, Italy and Austria-Hungary belonged to the Triple Alliance, while Britain, France and Russia belonged to a rival military bloc, the Triple Entente. The crux of the diplomatic crisis was that if Austria-Hungary went to war with Serbia, Serbia's ally Russia might then go to war with Austria-Hungary, which would trigger the entire alliance system.

After nearly one month of diplomatic maneuvering, the Austrian government felt it must act to protect its interests and to punish Serbia for its complicity in the Archduke's murder. At 6 p.m. on July 23, Austria-Hungary sent its ultimatum to the Serbian government in Belgrade.

The ultimatum called for Serbia to cease all agitation, peaceful or otherwise, in the empire's territory, and all propaganda directed against the empire within Serbia was to end. Additionally, Austria-Hungary demanded arrests and to be able to direct the investigation in Serbia, something the Serbs saw as a violation of their national sovereignty. Given the crime against the empire, the ultimatum was a reasonable reaction. However, sent almost one month after the event, it looked to most Europeans like what Remak calls “a large nation bullying a small one.”

Sir Edward Grey, the influential British foreign secretary called the ultimatum “the most formidable document I had ever seen addressed by one state to another that was independent.” The Russian foreign minister Sergey Sazonov said, “C'est la guerre européenne,” meaning, “This means a European war.”

A few days later, after Serbia rejected the ultimatum, the Austrian Emperor Franz Josef ordered the mobilization of his army for the purpose of invading Serbia. When the Russians mobilized to counter the threat, Germany mobilized against both Russia to its east and France to its west. By Aug. 4, the long delayed European war had finally arrived.

The First World War would last until 1918. Battling on multiple fronts, nearly 1.3 million subjects of the Austro-Hungarian empire would die in the conflict, while roughly 45,000 Serbians would perish. This is only a small portion of the total death toll from WWI.

Cody K. Carlson holds a master's degree in history from the University of Utah and currently teaches at Salt Lake Community College. He is also the co-developer of the History Challenge iPhone/iPad apps. Email: [email protected]